1. Field of the Invention
The present invention pertains to a method and apparatus for installing and levelling subsea drilling and/or foundation templates and the like using a semi-submersible drilling rig equipped with a heave compensator.
2. Background
In the art of developing subsea installations for production of hydrocarbons from formations below the seabed there have been numerous types of installations placed on the seabed including structures known as templates and the like. These structures are typically characterized by large skeletal frames which are used for supporting wellhead components and other apparatus used in conjunction with drilling and producing hydrocarbons from subsea wells.
There are several problems associated with handling the relatively large structures known as templates. The process of loading, transporting and installing a subsea template using a semi-submersible drilling rig or other floating structure has presented several problems in the overall procedure of handling the templates from the point of embarkation to the final installation and levelling procedure.
In particular, it is difficult to properly position or level a subsea template from a floating structure unless sea conditions are totally calm, a rare occurrence in many offshore oil fields, particularly areas such as the North Sea. The levelling procedure is, however, desirable and necessary in order that the template or other related structure be properly oriented with respect to a floating drill rig, for example, which will be working through and utilizing the template. Moreover, a levelling procedure using a floating vessel such as a semi-submersible drilling rig, which may be constantly changing its elevation with respect to the seabed as a result of sea conditions, has presented several problems in the art of installing subsea templates. However, the present invention provides an improved method and apparatus for installing and properly levelling a subsea template or the like using a floating drilling rig or a similar floating vessel equipped with hoisting apparatus. In particular, the present invention pertains to an improved method and apparatus using a semi-submersible floating drilling rig equipped with a heave compensator or the like.